1. Field of the Invention
The present invention relates to flat panel display devices and, more particularly, to spacers for a high voltage flat panel display.
2. Description of the Related Art
An emissive vacuum flat-panel display typically has front and rear panels held in place by a supporting frame around the periphery of the panels. Examples of flat panel displays can be found in European Patent Application number 94301384.7, entitled "A Flat Panel Display", published Sep. 7, 1994, and in European Patent Application number 94306859.3, entitled "Focusing and Steering Electrodes for Electron Sources", published Mar. 29, 1995, both having the same inventor, Huei Pei Kuo.
A thin layer of light-emissive material such as phosphor is typically deposited on the front panel of the display. The phosphor emits visible light when bombarded by energetic electrons. The back panel of the display, in turn, has an array of electron sources. The electron sources accelerate electrons towards the front panel to bombard and excite the phosphor material on the front panel. When appropriate signals are applied to the electron-source array and the phosphor screen, light emitted from the phosphor screen is modulated to display desired information patterns. If an array of field emission electron source is used as the electron sources, such a display is commonly known as a Field Emission Display ("FED").
The front and back panels of a vacuum flat-panel display are typically made of transparent glass of a thickness of approximately 1 mm. The supporting frame around the periphery is used to maintain a distance of a few millimeters between the panels. The panels and the frame form a vacuum envelope which is evacuated to a vacuum better than approximately 10.sup.-7 Torr. This causes the panels to be subjected to an atmospheric pressure of approximately 1 Kg/cm.sup.2. For a display with a screen dimension greater than approximately 1 cm by 1 cm, additional support structures, or spacers are required to prevent the panels from being distorted or destroyed under the atmospheric pressure.
Basically, three types of spacer designs are used by the prior art: spheres, cylinders and walls. Although each design has one or more advantage, inherent to each design is one or more undesirable disadvantage.
Spherical spacers are ideally shaped to withstand compressive stress; are easy to manufacture and displays using spherical spacers are easy to assemble. However, because the size of sphere equals the spacing between the panels, the sphere becomes visible when the panel spacing is greater than 200-300 .mu.m.
Cylindrical post spacers have an excellent compressive strength. They also have a small lateral dimension, therefore the posts remain invisible for larger spacing between the panels than is possible in the case of spherical spacers. Cylindrical posts have poor buckling strength, however, and displays using cylindrical posts can be difficult to assemble.
Finally, wall spacers have an excellent stiffness in the direction along wall and are easily fabricated. On the other hand, wall spacers have a poor buckling strength in the direction perpendicular to the wall; displays using wall spacers are difficult to assemble; and the wall spacers are difficult to make invisible.
In a field emission display where high-voltage phosphor is used, the minimum spacing between the front and rear panel is approximately 1 mm for a 5 Kilovolt operation. The spherical spacer is too large and not suitable for this application. The cylindrical and wall spacers can be used, but suffer from the shortcomings listed above.
Thus, it can be seen that the poor strength, visibility and assembly difficulty limits of current technology spacers for flat-panel display devices limits the use of these devices in many applications.
Therefore, there is an unresolved need for a spacer for a high-voltage flat panel display that will significantly improve the strength, invisibility and assembly limits of current technology spacers.